This invention relates to the field of lasers and more specifically to the field of injection lasers, whether used on oscillator light sources or amplifiers.
Initial interest in the laser was, in part, due to well-defined emission modes resulting in exceedingly narrow linewidth output. However, this very characteristic severely limits the available wavelengths of coherent light sources.
Because optical communications systems are being designed to transmit at several different wavelengths, there now exists a need for lasers operating over a wide range of wavelengths, and particularly for semiconductor injection lasers having these properties. Since these lasers are compact, light in weight and are easily produced on a mass production scale, semiconductor injection lasers play an important role as the light source in both optical communications and optical information processing systems.
Generally, a typical optical communications system transmitting at several different wavelengths first couples the outputs from several lasers to several optical fibers. Then, the outputs from the optical fibers are coupled into a single transmission optical fiber. The total accumulated optical coupling loss in such a system tends to be large.
One technique aimed at reducing this coupling loss involves placing several lasers on the same substrate. Nevertheless, this necessitates using complicated waveguide structures to couple the light from the spatially separate lasers into a single fiber. As a result, these devices still possess high coupling losses.